146 lines
2 KiB
ArmAsm
146 lines
2 KiB
ArmAsm
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.define .dvi4
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! 32 bits integer divide and remainder routine
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! Bit 0 of a-reg is set iff quotient has to be delivered
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! Bit 7 of a-reg is set iff the operands are signed, so:
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! Expects in a-reg: 0 if called by rmu 4
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! 1 if called by dvu 4
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! 128 if called by rmi 4
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! 129 if called by dvi 4
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! Expects on stack: divisor
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! dividend
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! Yields on stack: quotient or remainder
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.dvi4: pop h
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shld .retadr
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mov h,b
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mov l,c
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shld .bcreg
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sta .areg
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pop h ! store divisor
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shld block3
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xchg
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pop h
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shld block3+2
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dad d
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jc 1f
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mov a,l
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ora h
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cz eidivz ! trap if divisor = 0
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1: pop h ! store dividend
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shld block1
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pop h
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shld block1+2
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lxi h,0 ! store initial value of remainder
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shld block2
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shld block2+2
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mvi b,0
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lda .areg
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ral
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jnc 2f ! jump if unsigned
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lda block1+3
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ral
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jnc 1f
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mvi b,129
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lxi h,block1
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call compl ! dividend is positive now
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1: lda block3+3
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ral
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jnc 2f
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inr b
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lxi h,block3
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call compl ! divisor is positive now
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2: push b ! save b-reg
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mvi b,32
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dv0: lxi h,block1 ! left shift: block2 <- block1 <- 0
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mvi c,8
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xra a
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1: mov a,m
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ral
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mov m,a
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inx h
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dcr c
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jnz 1b
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lxi h,block2+3 ! which is larger: divisor or remainder?
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lxi d,block3+3
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mvi c,4
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1: ldax d
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cmp m
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jz 0f
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jnc 3f
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jmp 4f
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0: dcx d
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dcx h
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dcr c
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jnz 1b
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4: lxi d,block2 ! remainder is larger or equal: subtract divisor
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lxi h,block3
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mvi c,4
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xra a
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1: ldax d
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sbb m
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stax d
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inx d
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inx h
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dcr c
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jnz 1b
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lxi h,block1
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inr m
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3: dcr b
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jnz dv0 ! keep looping
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pop b
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lda .areg ! quotient or remainder?
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rar
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jnc 4f
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! for dvi 4 and dvu 4 only:
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mov a,b
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rar
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lxi h,block1 ! complement quotient if divisor
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cc compl ! and dividend have different signs
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lhld block1+2 ! push quotient
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push h
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lhld block1
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push h
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jmp 5f
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! for rmi 4 and rmu 4 only:
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4: mov a,b
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ral
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lxi h,block2
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cc compl ! negate remainder if dividend was negative
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lhld block2+2
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push h
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lhld block2
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push h
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5: lhld .bcreg
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mov b,h
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mov c,l
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lhld .retadr
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pchl
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! make 2's complement of 4 bytes pointed to by hl.
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compl: push b
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mvi c,4
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xra a
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1: mvi a,0
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sbb m
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mov m,a
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inx h
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dcr c
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jnz 1b
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pop b
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ret
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